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死鎖定義
死鎖是指兩個或者多個線程被永久阻塞的一種局面，產生的前提是要有兩個或兩個以上的線程，并且來操作兩個或者多個以上的共同資源；我的理解是用兩個線程來舉例，現有線程A和B同時操作兩個共同資源a和b，A操作a的時候上鎖LockA,繼續執行的時候，A還需要LockB進行下面的操作，這個時候b資源在被B線程操作，剛好被上了鎖LockB，假如此時線程B剛好釋放了LockB則沒有問題，但沒有釋放LockB鎖的時候，線程A和B形成了對LockB鎖資源的爭奪，從而造成阻塞，形成死鎖；具體其死鎖代碼如下：
public class MyDeadLockTest {
public static void main(String[] args){
Object obj1 = new Object();
Thread thread1 = new Thread(new DeadRes(true,obj1));
Thread thread2 = new Thread(new DeadRes(false,obj1));
thread1.start();
thread2.start();
}
}
class DeadRes implements Runnable{
boolean flag;
Object obj;
public DeadRes(boolean flag, Object obj1) {
this.flag = flag;
this.obj = obj1;
}
@Override
public void run() {
if(flag){
synchronized (DeadRes.class){
System.out.println(Thread.currentThread().getName()+" acquie lock is DeadRes.class");
synchronized (obj){
System.out.println(Thread.currentThread().getName()+" acquie lock is obj");
}
}
}else{
synchronized (obj){
System.out.println(Thread.currentThread().getName()+" acquie lock is obj");
synchronized (DeadRes.class){
System.out.println(Thread.currentThread().getName()+" acquie lock is DeadRes.class");
}
}
}
}
}
執行結果如下圖：
Thread-1 acquie lock is obj Thread-0 acquie lock is DeadRes.class
當然每次執行的結果不一樣，有可能是一種和諧狀態，沒有發生死鎖，此時為保證每次死鎖，可以讓run()方法中，執行while(true)循環，這樣保證了每次必定發生死鎖；當然實際應用中，我們應該盡量避免死鎖，當有多線程操作多個共同資源的時候，避免發生同一鎖對象的同步嵌套。
線程間的通訊—-生產者與消費者模式
1、讓兩個線程交替進行操作，當生產了一個數字后，緊接著消費一個，首先采用Object對象中的wait-notify來實現，具體代碼如下:
public class ThreadProConsume {
public static void main(String[] args){
Product product = new Product();
Thread thread1 = new Thread(new Producer(product));
Thread thread2 = new Thread(new Consumer(product));
thread1.start();
thread2.start();
}
}
class Product{
String name;
private int count = 1;
boolean flag = false;
public synchronized void set(String name){
if(flag){
try {
this.wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
this.name = name +"--"+count++;
flag = true;
System.out.println(Thread.currentThread().getName()+" produce num : "+this.name);
this.notify();
}
public synchronized void out(){
if(!flag){
try {
this.wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
System.out.println(Thread.currentThread().getName()+" consume num is : "+this.name);
flag = false;
this.notify();
}
}
class Producer implements Runnable{
Product res;
public Producer(Product product) {
this.res = product;
}
@Override
public void run() {
while(true){
res.set("guyue");
}
}
}
class Consumer implements Runnable{
Product res;
public Consumer(Product product) {
this.res = product;
}
@Override
public void run() {
while(true){
res.out();
}
}
}
執行結果如圖：
Thread-1 consume num is : guyue--3938 Thread-0 produce num : guyue--3939 Thread-1 consume num is : guyue--3939 Thread-0 produce num : guyue--3940 Thread-1 consume num is : guyue--3940 Thread-0 produce num : guyue--3941 Thread-1 consume num is : guyue--3941
當超過兩個以上線程操作的時候，這里需要在set()與out()方法中的if判斷改為while，并且notif方法，改為notifyAll()，這樣多個線程操作的時候，便可以交替進行，具體代碼如下：
public class ThreadProConsume {
public static void main(String[] args){
Product product = new Product();
Thread thread1 = new Thread(new Producer(product));
Thread thread3 = new Thread(new Producer(product));
Thread thread2 = new Thread(new Consumer(product));
Thread thread4 = new Thread(new Consumer(product));
thread1.start();
thread3.start();
thread2.start();
thread4.start();
}
}
class Product{
String name;
private int count = 1;
boolean flag = false;
public synchronized void set(String name){
while(flag){
try {
this.wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
this.name = name +"--"+count++;
flag = true;
System.out.println(Thread.currentThread().getName()+" produce num : "+this.name);
this.notifyAll();
}
public synchronized void out(){
while (!flag){
try {
this.wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
System.out.println(Thread.currentThread().getName()+" consume num is : "+this.name);
flag = false;
this.notifyAll();
}
}
執行結果如下：
Thread-0 produce num : guyue--50325 Thread-2 consume num is : guyue--50325 Thread-1 produce num : guyue--50326 Thread-3 consume num is : guyue--50326 Thread-0 produce num : guyue--50327 Thread-2 consume num is : guyue--50327 Thread-1 produce num : guyue--50328 Thread-3 consume num is : guyue--50328
2、采用Lock-Condition方法實現如下：
class Product{
String name;
private int count = 1;
boolean flag = false;
Lock lock = new ReentrantLock();
Condition conditon = lock.newCondition();
public void set(String name){
try{
lock.lock();
while(flag){
conditon.await();
}
this.name = name +"--"+count++;
flag = true;
System.out.println(Thread.currentThread().getName()+" produce num : "+this.name);
conditon.signalAll();
}catch (Exception e){
}finally {
lock.unlock();
}
}
public void out(){
try{
lock.lock();
while(!flag){
conditon.await();
}
flag = false;
System.out.println(Thread.currentThread().getName()+" consumer num is : "+this.name);
conditon.signalAll();
}catch (Exception e){
}finally {
lock.unlock();
}
}
}
執行結果如下：
Thread-0 produce num : guyue--20305 Thread-3 consumer num is : guyue--20305 Thread-1 produce num : guyue--20306 Thread-2 consumer num is : guyue--20306 Thread-0 produce num : guyue--20307 Thread-3 consumer num is : guyue--20307 Thread-1 produce num : guyue--20308 Thread-2 consumer num is : guyue--20308
以上就是本文關于Java編程之多線程死鎖與線程間通信簡單實現代碼的全部內容，希望對大家有所幫助。關于Java多線程以及線程間通信的例子，本站還有幾篇文章可以參考：
詳解java中的互斥鎖信號量和多線程等待機制、Java多線程編程小實例模擬停車場系統、Java網絡編程基礎篇之單向通信
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